Wednesday, March 12, 2014

Musings on Deep Time: it's all about the fizz

Musings on Deep Time
Many of us have heard how old the Earth is, how old the solar system is, and perhaps even how old the universe itself is. Maybe you have even seen a timescale laid out, showing how if the age of the Earth was compared to one year, man and all his history wouldn't appear until December 31st. In fact, the other night, during the relaunch of the Cosmos television series made famous by Carl Sagan, the new host Neil DeGrasse Tyson did that, comparing the age of the universe to an Earth year. On that scale, everything we have ever done fit into the very last second of December 31st! In this same episode, DeGrasse Tyson gave a very brief description of the far future of the universe, and that got me thinking. I deal a lot with geological time in my job, so I'm used to thinking in tens of thousands of years, in millions of years, and occasionally in billions of years. Because of my past work with NASA and time at Caltech and MIT, I'm also interested in astronomical timescales, so even tens of billions of years are 'comfortable.' I was not prepared for the cosmological timescale. And neither are you. I guarantee it.
1. It's all about the fizz
You have probably seen a timeline of the history of the universe that begins with the Big Bang, proceeds with all that star and galaxy formation stuff, and ends up with the large scale structures we see today. It struck me that these timelines always stop at the present. What about the next 20 billion years? What about the next 2,000 billion years? What do we think is going to happen? And so I went looking for papers on the subject. It turns out there aren't very many. Apparently such conjectures aren't good for publication records or tenure. And there's good reason for that - the various scenarios have large error bars, and depend on answers to questions we still haven't answered, like how long does matter last? How large can the universe get? How, exactly, do black holes die? How is mass related to gravity? What the heck is this 'dark matter' and 'dark energy' stuff? It turns out that those questions are much more complicated than we ever expected, and the answers (where we have any) are very weird.
Anyhow. I shall sidestep all those complications, and cut to the chase. First: how long will the universe last? An unimaginably long time. Well, possibly even forever. But it's a forever I never want to see: it's very likely a very cold, very dark place. The only things in it are a few flecks of imperceptible light, so dim and weak that nothing could ever detect them. Every few duotrigintillion years (we'll get back to that) you might come across an electron. That's it. That's all. No trace of the Earth, the Sun, or of anything we ever did. No trace of any other civilization on any other star, on any other galaxy. Absolutely nothing. It will all be erased. The ultimate void. Perhaps Genesis had it backwards.
Conclusion: very boring. Stultifying. So let's tell this story backwards, and find the very last 'really exciting' thing that happened. It turns out that label belongs to the disappearance of the last black hole. Yes, we think they disappear. They might be fearsome juggernauts in our universe right now, destroying entire stars, spinning whole galaxies, and fueling all kinds of science fiction nonsense, but in the end, they will simply fade out of existence. How the heck does that happen? Aren't they supposed to swallow everything forever? So here's the first little piece of weirdness I promised: black holes actually fizz. Stephen Hawking came up with this startling conclusion. I'll deal with the details somewhere else, but the essence of it is that at a very, very slow rate, black holes give off energy, and each time they do, they shrink a bit. If you wait long enough, even the biggest black hole imaginable will eventually evaporate. How long? A googol years. So there you go: you finally have a use for that word, googol. No, not Google. Googol. One duotrigintillion. A one followed by a hundred zeros: 10,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000,­000 years.
How do we wrap our brains around a number like this? Here's a little taste of how hard that is: let's try the DeGrasse Tyson trick, and make January 1 be year 0, and midnight December 31st be a googol years later. Now we've got a scale for the 'exciting' portion of the universe's lifetime laid out before us. Let's find out where man sits! And… you can't find it. Every single day looks the same: fizzy black holes. They get bigger as you go backwards, but even there, on January 1, the very beginning of our universal timescale, the whole day seems to be full of really boring, gassy black holes! What about the first second of January 1? Same. What about the first millisecond? Same. And so on. Microseconds, nanoseconds, femtoseconds, attoseconds, yoctoseconds, and beyond. We keep trying to find Earth, even our Sun, our Galaxy, anything. But on this scale, the scale of black hole lifetimes, of a googol years, even something so unimaginably old as the Earth, the Sun or even the 'TODAY' mark--13.8 billion years from the start--is too close to the beginning to see. So, on our cosmic calendar, before we even had time to look at our watches, everything we have ever known about, even our Sun, and even the very last star ever to shine, is gone before we know it, and we still have 365 days of fizzing to go.
Can't we try a different trick? How about laying out that same googol years in a line, from here out to where Voyager 1 is, about three times as far from the Sun as Pluto, or 20 billion kilometers? Now, surely we should be able to see something other than fizz? Nope. Even before you have moved along that line over the width of one atom, everything is all fizz! It turns out that on that incredibly long line marking out the time from the Big Bang to the evaporation of the last black hole, the little mark for 'TODAY' is only 1/60,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000th of the width of an atom from the start. A googol years is a very, very, very long time, and most of it is really, really, really boring. However, remember that even this was not as boring as the 'cold dark forever' I described previously, which might last a googol googol years!
Next: we zoom in so we can finally see something, sixty orders of magnitude, to the end of normal matter, at one tredecillion years, or a one followed by forty-two zeros: only 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000 years! After wrapping our brains almost around a googol, this ought to be easy. Right?